The present invention relates to temperature control in an electric motor, more particularly a fractional horsepower permanent magnet direct current (PMDC) motor having a positive temperature coefficient resistor in its electric circuit.
Small PMDC motors are often used in situations when they may be caused to stall while power is still applied to the motor. A high current passes through the motor while it is stalled and this can result in overheating of the motor components with risk of damage to the motor and the possibility of fire when the motor is used in confined spaces such as in automobiles.
Temperature sensitive switches using bimetallic contacts or the like can be used to break the motor circuit when the temperature rises to an unacceptable level. However, such switches require that the motor size be increased to accommodate them in the motor end cap, or a device may be placed on the outside of the motor where it is prone to damage.